1. Field of the Invention
The present invention relates to a high-voltage detection circuit of a semiconductor integrated circuit, and particularly to a high-voltage detection circuit for setting a high voltage at a high-accuracy level used for a flash memory.
2. Description of the Prior Art
Generally, in a nonvolatile flash memory of a semiconductor integrated circuit, a high voltage level is necessarily used for extraction and injection of electric charges, and the high voltage level must be accurately set in order to accurately control electric charges when extracting or injecting electric charges from or into a floating gate of a memory cell.
In a conventional flash memory and the like device, a two-power-source configuration is used for obtaining, for example, a high voltage Vp of 12V from the outside of a chip and an internally-generated high voltage Vcc of 5V as the two power-source voltages. In recent years, however, such a two-power-source configuration is changed to a single power-source configuration as a technical trend as the power-source voltage Vcc is reduced, and the single power-source configuration is now mainly used for obtaining Vcc of 5V or 3V as an internally-generated high voltage.
According to this technical trend, for example, a charge-pump-type high-voltage generation circuit is used as a high-voltage power source. For example, when 3 V is used as a high voltage Vcc and a threshold voltage Vth is 0.6 V, a strive zone ranging between 0.6 and 2.6 V is used as an easily-controllable range.
This high voltage Vcc is generated by a high-voltage generation circuit such as a charge pump circuit in a device. However, since a voltage generated by a high-voltage generation circuit is fluctuated due to an operation condition of the circuit such as a power-source voltage level or temperature, the operation of a high-voltage generation circuit is controlled using a high-voltage detection circuit for detecting a high voltage.
FIG. 7 is a circuit diagram showing a configuration of a conventional high-voltage detection circuit and the configuration and operations of the circuit are disclosed in Japanese Patent Laid-Open No. 19200/2000 as a prior art thereof.
As shown in FIG. 7, a high-voltage detection circuit is provided with a resistor element 701 having a resistance value of R5 and a resister element 702 having a resistance value of R6 connected in series between an output terminal 700 of a high-voltage generation circuit and a ground potential GND line, a comparison circuit 703 and an inverter 708. The comparison circuit 703 includes P-channel MOS transistors 704 and 705 and N-channel MOS transistors 706 and 707.
The resistor elements 701 and 702 constitute a partial-voltage circuit or potential divider, and when assuming the potential of the output terminal 700 of the high-voltage generation circuit is set as VP and resistance values of the resistor elements 701 and 702 are set as R5 and R6 respectively, the partial-voltage potential VO of a node N1 between the resistor elements 701 and 702 becomes VO=VPxc2x7R6/(R5+R6).
The MOS transistors 704 and 706 and the MOS transistors 705 and 707 are respectively connected in series between the line of the power-source potential Vcc and the line of the ground potential GND. Gates of the MOS transistors 704 and 705 are both connected to the drain of the MOS transistor 704 and thus the MOS transistors 704 and 705 constitute a current mirror circuit. The partial-voltage potential VO on the node N1 is applied to the gate of the MOS transistors 706 and a reference potential Vref is applied to the gate of the MOS transistors 707. The drain of the MOS transistor 705 serves as an output node 703a of the comparison circuit 703 and an output signal of the comparison circuit 703 is inverted by the inverter 708 and the resultant output is generated as a high-voltage detection signal /DE.
When the potential VP is lower than a target potential and the potential VO is lower than the reference potential Vref, the conduction resistance value of the MOS transistor 706 becomes larger than that of the MOS transistor 707, a node 703a becomes L-level, and the high-voltage detection signal /DE becomes H-level. When VP exceeds the target potential and VO becomes higher than Vref, the resistance value of the MOS transistor 706 becomes smaller than that of the MOS transistor 707, the node 703a becomes H-level, and the signal /DE becomes L-level. The high-voltage generation circuit is activated when the signal /DE becomes H-level, and the high-voltage generation circuit is deactivated when the signal /DE becomes L-level. Thus, the potential of the output terminal 700 is kept at the target potential.
In the above conventional high-voltage detection circuit, the voltage conversion efficiency xcex94VO/xcex94VP becomes xcex94VO/xcex94VP=R6/(R5+R6). Since R6/(R5+R6) less than 1, the voltage conversion efficiency is lowered. Lowering of the voltage conversion efficiency deteriorates the detection accuracy of the high-voltage detection circuit, and moreover lowers the setting accuracy of a voltage level of high-voltage.
For example, when assuming VP as 9V and the reference potential Vref as 1.5 V, the voltage conversion efficiency becomes 1.5/9=R6/(R5+R6)=1/6. This indicates that the detected VP is fluctuated greatly by 0.1xc3x976=0.6 V when Vref is fluctuated by 0.1 V due to dispersion and the like.
Thus, in the conventional example, a comparatively low potential such as Vref=1.5 V is used as the reference voltage Vref. However, the present invention is made by considering that a voltage conversion efficiency becomes 4.5/9=R6/(R5+R6)=1/2 by making it possible to set Vref to, for example, 4.5 V, so that the detected VP becomes 0.1xc3x972=0.2 V to a Vref dispersion of 0.1 V, and the fluctuation can be decreased to 1/3 compared to the conventional example.
The present invention is made to solve the above problems and its object is to provide a high-voltage detection circuit capable of improving a voltage detection accuracy and realizing a stable voltage-detection accuracy by setting a reference voltage Vref to a comparatively high potential.
To achieve the above mentioned object, the present invention realizes a high-voltage detection circuit to have a high voltage-detection accuracy by constituting the high-voltage detection circuit so as to use a high voltage level output from a high-voltage generation circuit for the power source of a reference-voltage generation circuit in order to set the reference voltage Vref to a comparatively high voltage level.
According to the present invention, a high-voltage detection circuit detects a high voltage output from a high-voltage generation circuit in a semiconductor memory. The high-voltage detection circuit includes: a high-voltage drop circuit which drops the high voltage output of the high-voltage generation circuit and generates a dropped voltage; and a reference voltage generation circuit which receives the high voltage output of the high-voltage generation circuit to be used as an input voltage source and generates a reference voltage. The high-voltage detection circuit further includes a comparison circuit which compares the dropped voltage output of the high-voltage drop circuit with the reference voltage output of the reference-voltage generation circuit and thereby controls a high-voltage level of the high-voltage generation circuit.
With the above mentioned configuration, it is possible to provide a high-voltage detection circuit capable of setting a reference voltage obtained from a reference-voltage generation circuit to a potential higher than that of a conventional circuit, improving a voltage detection accuracy by using a high potential voltage output of the high-voltage generation circuit for the power source of the reference-voltage generation circuit, and realizing a stable voltage-detection accuracy.